The present invention relates to a bearing arrangement including a plain bearing consisting of a laminated body of a bearing layer and a backing metal supporting the bearing layer, and more particularly to a bearing arrangement composed of a bearing housing of the type that two halves are coupled together by means of bolts, and a half-split type or wrapped bush type of plain bearing interpored between a rotary shaft to be supported and the bearing housing with a predetermined interference and consisting of a laminated body of a bearing layer and a backing metal supporting the bearing layer.
In an internal combustion engine, the opposite end portions (smaller end portion and larger end portion) of a connecting rod connecting a piston with a crank shaft form bearing housings of bearing arrangements respectively supporting a piston pin and the crank shaft (crank pin). The smaller end portion forms an integral type of bearing housing having a through-hole, and a plain bearing for supporting the piston pin is press-fitted into the through-hole. The larger end portion forms a bearing housing of the type of coupling two halves together by means of bolts, and within this bearing housing is fitted a half-split type plain bearing with a predetermined interference (crush height amount).
Now, in order to contemplate to realize a high output power, a high speed and a light weight of an engine, examples of making a connecting rod of aluminum alloy are being increased. However, in the case of the bearing housing made of aluminum alloy (the smaller end portion and the larger end portion of the connecting rod made of aluminum alloy), since a coefficient of thermal expansion (about 23.times.10.sup.-6) of the connecting rod is nearly twice as large as a coefficient of thermal expansion (about 12.times.10.sup.-6) of a bearing made of ordinary steel, it is necessary to compensate for the difference of thermal expansion between the bearing housing and the bearing resulted from temperature rise, and so, various countermeasures have been taken.
The countermeasure disclosed in Laid-Open Japanese Utility Model Specification No. 56-4021 (1981) is one example, in which a bush made of ferrous metal (for instance, a bush made of austenitic stainless steel) having a coefficient of thermal expansion equal or close to that of the aluminum alloy is press-fitted into the smaller end portion of the connecting rod made of aluminum alloy. In this example, since the coefficient of thermal expansion (about 18.times.10.sup.-6) of the bush made of austenitic stainless steel is considerably large as compared to that of ordinary steel and has a value close to the coefficient of thermal expansion of aluminum alloy, even if the interference of the bush caused by the smaller end portion forming a bearing housing is chosen smaller than the interference for the bush made of ordinary steel (that is, even if the fastening stress of the bearing housing is made small), a following property of the bush to the thermal expansion deformation of the smaller end portion can be insured. However, when the smaller end portion made of aluminum alloy and the bush made of austenitic stainless steel has expanded and deformed, there is a possibility that the clearance between the bush and the shaft made of ordinary steel may increase, and also, there is a shortcoming that as the austenitic stainless steel is poor in thermal conductivity as compared to ordinary steel, heat transmission between the shaft and the smaller end portion cannot be achieved smoothly.
Now let us imagine the case where the inventive concept disclosed in the above-referred Laid-Open Japanese Utility Model Specification No. 56-4021(1981) is applied to a bearing housing formed by coupling together two halves made of aluminum alloy by means of bolts made of ordinary steel as is the case with the larger end portion of the connecting rod, and a cylindrical bush made of austenitic stainless steel has been interposed between the shaft made of ordinary steel and the bearing housing. When a temperature has risen, thermal expansion of the respective halves of the bearing housing is supressed by the bolts in the axial direction of the bolts, but is allowed in the direction perpendicular the axes of the bolts, and so, as a result the bearing housing is deformed into a laterally elongated shape. At this moment, since the bush has a cylindrical shape, a following property thereof to the bearing housing which deforms into a laterally elongated shape, is poor, and so, there is a possibility that an increased clearance may arise between the bearing housing and the bush at the positions close to the bolts.
In the case of such a bearing housing formed by coupling together two halves by means of bolts in the above-described manner, if a half-split type plain bearing is fitted into the bearing housing with a predetermined interference as described above, then this plain bearing can deform well following to the laterally elongated deformation of the bearing housing. However, since the plain bearing would repeat deformation between a truly circular shape and a laterally elongated shape according to temperatures variations, this plain bearing is required to have a good fatigue characteristic.
While a plain bearing made of a laminated metal strip formed by providing a bearing alloy layer made of white metal, Kelmet metal, aluminum alloy, etc. on a backing metal made of steel has been known as disclosed in, for example, Laid-Open Japanese Utility Model Specification No. 56-13407 (1981), even with such plain bearing the above-described various problems would still remain with respect to the backing metal made of steel.